Process for the preparation of acrylic manmade fiber

ABSTRACT

A composite acrylonitrile filament is passed through a hot water bath substantially without relaxation and with a tension of less than 0.005 grams per denier and at a substantially unchanged speed relative to the spinning speed.

United States Patent Chozo Nakayama Fuji-shl;

Toshlo Ohiuka, Fujl-shi; I'Iiroshi Yokoyama, Firil-shl; Hideo Sate, Fuji-shi; Koulchi Ashikaga, Yoshihara-shi; Takashi Sakakiyam, Yoshihara-shi; Kouji Kitashima, Fuji'shi, all of Japan [72] Inventors Continuation of application Ser. No. 540,388, Apr. 5, 1966, now abandoned. This application Oct. 13, 1969, Ser. No. 866,178

[54] PROCESS FOR THE PREPARATION OF ACRYLIC MANMADE FIBER 10 Claims, 4 Drawing Figs.

[52] U.S.Cl 264/168,

[51] Int. Cl v. D0ld 5/22, DOZg 1/00 [50] Field of Search 264/171, 168; 161/173 [56] References Cited UNITED STATES PATENTS 3,066,006 11/1962 Sonnio 8/151.2 3,264,705 8/1966 Kovarik 28/76 3,330,896 7/1967 Fujita et a1 264/103 3,384,694 5/1968 Nakayama et a1. 264/211 3,397,426 8/1968 Fujita et a1 264/171 X 3,405,517 10/1968 Anahara et al. 57/157 TS 3,438,192 4/1969 Ryan 264/168 3,471,605 10/1969 Matsui et a1. 264/171 2,333,279 11/1943 Truesdial 28/71.3

Primary Examiner.lay H. Woo Att0rneyWaters, Roditi, Schwartz & Nissen ABSTRACT: A composite acrylonitrile filament is passed through a hot water bath substantially without relaxation and with a tension ofless than 0.005 grams per denier and at a substantially unchanged speed relative to the spinning speed.

PATENTEU N0v30 |97l 3 624, 195

sum 1 OF 3 PATENTEnunvaolan 3624.195

sum 2 0F 3 for) X 1 METHALL) SULFO/V/C' ACID 0/? ACRYLATE 0/? METHACRYLA 75 0F SUL FOALCOHOL m0/%) 2 1 TOTAL OF/JCRYLAM/DE A/VD ACRYLATES 0/? METHACRYLATES (mo/ y 1 ACRYLATES 0/? METHACRYLATES (/770/%) PROCESS FOR THE PREPARATION OF ACRYLIC MANMADE FIBER This is a continuation of Ser. No. 540,388, filed Apr. 5, l966, and now abandoned.

This invention relates to a process for the preparation of 5 acrylic manmade fiber. More particularly, the invention relates to a process for preparing acrylonitrile composite fiber according to a wet spinning method using an inorganic solvent preferably a sufficiently refined 60 percent or higher concentrated nitric acid aqueous solution.

There is much written concerning the fact that two or more kinds of polymers which differ from each other in shrinking characteristic are bonded togethereccentrically in the same single fiber section to obtain a fiber having the ability to develop three-dimensional natural crimp (hereinafter, referred to as composite fiber"), and it is also well known that a composite fiber can be obtained from acrylonitrile polymers.

We have previously done exhaustive research on the process of preparing acrylonitrile composite fiber according to a wet spinning method using a concentrated inorganic solution, especially concentrated nitric acid as solvent. As a result, we have found that composite fibers obtained by employing known polymer combinations and by using concentrated nitric acid as solvent in the preparation of acrylonitrile composite fibers have various defects. It was also found that it is necessary to employ very specific polymer combinations in order to obtain composite fibers excellent in practical properties and esthetic qualities and we have invented a process for the preparation of novel acrylonitrile composite fibers (hereinafter, referred to as our prior invention"). Acrylonitrile fibers of the present invention mean those which are at least 85 percent acrylonitrile by weight, the balance being other comonomers.

One feature of the composite fibers prepared according to the process of our prior invention was that the fibers substantiality was greatly increased as compared with composite fibers otherwise prepared.

Generally, fibers prepared according to wet spinning methods tends to have unsatisfactory substantiality when compared with fibers prepared according to dry spinning methods. Further, in wet spinning methods, said tendency is seen more in cases where inorganic solvents are used than in cases where organic solvents are used. In cases where nitric acid as solvent, said tendency is conspicuous and it is necessary to take care in selecting the conditions. In the preparation of composite fibers, such a tendency is noted even more clearly and to a magnified extent and the use of known polymer combinations can give only very unsatisfactory composite fibers. Herein increase in substantiality" means an increase in fiber transparency, increase in fiber luster, increase in dyed fibers brightness, disappearance of pastel color, decrease in damage upon fiber after-processing, decrease in number of the socalled shortened fiber fly and so on. The substantiality of a fiber has very important significance for the practical properties and esthetic qualities of fiber. The above-mentioned properties for judging substantiality of fiber are difficult to determine quantitatively except for the number of fly, but a difference in substantiality between fiber samples is apparent upon visual inspection. Therefore, the effect of the present invention on the commodity value of the product will be easily understood.

One feature of the composite fibers prepared according to the process of our prior invention resides in the behavior ofar ticles made from said fiber, such as bulky yarns, knittings, fabrics and the like, when subjected to stress. In particular, the strain produced by applying stress can recover at very high rate after removing the stress and the disappearance of strain is very fast not only after washing the article but also after nearly leaving it at room temperature.

The other advantages of our prior invention will be mentioned later again in connection with the present invention. In short, the gist of our prior invention was based on our discovery that in cases where as a solvent, an inorganic solvent such as concentrated nitric acid, it was possible to prepare composite fibers excellent in practical properties only by using very specific and limited compositions of polymers.

In particular, according to our prior invention, when using nitric acid as solvent, two kinds of polymers A and B comprising the composite fiber were required to satisfy the following requirements: In A: x and r are within the area surrounded by l, 2 and 3 in FIG. 3 and t and z are within the area surrounded by 7 and 8 including 7 in FIG. 4. In B: x and y are within the area surrounded by I, 2 and 6 in FIG. 3. wherein x is the percentage by weight of methallyl sulfonic acid or acrylates esters or/and methacrylates of sulfoalcohols contained in the polymers, y is the weight percentage of acrylates or/and methacrylates contained in the polymer; and t is the combined weight percentage of acrylates or/and methacrylates and acrylamide contained in the polymers.

. If weight percentage of acrylamide contained in the A component is designated as 1, the following relative formulae must also be satisfied between t and z:

t-zZO (7) And it was further necessary that the remaining part in A component, and B component are acrylonitrile.

For instance, in the case of preparing a composite fiber by using a combination of A component in which .r and I are below line I in FIG. 3, and B component, the substantiality of the fiber is considerably decreased, and a fiber liable to be damaged by mechanical impact is obtained, production of shortened fiber, the so-called fly is increased in the afterprocessing step and the obtained spun yarn tends to be degraded. In addition, it is often observed that when dyed with cationic dyestufi", the finished appearance lacks clearness and luster. The smaller the combined amount of (y+z) in the composition when t and z are within the area surrounded by lines 7 and 8 and on line 7 in FIG. 3 and x and t are within the area surrounded by lines I, 2 and 3 and the two axes becomes, the greater the extent of said disadvantage is and if compositions of the both components are close to each other, crimps in a practical sense are not developed. Further, in the case when .r and t ofA component is below line I in FIG. 3 and simultaneously x and y in B component are below line 6 in FIG. 3, disadvantages are even greater and when both y and z are small, it is difficult to obtain satisfactory yarn even in the spinning step.

Further, when x and y of B component are above line I in FIG. 3, or when x and t of A component are below line I in FIG. 3 and simultaneously x and y in B component are above line 1 in FIG. 3, uneven dye is liable to be produced when the fiber is subjected to dyestuff, forfeiture of luster is liable to occur when dyed to a dark color and damage is great when the fiber is subjected to a repeating load.

Further, when x and I of A component is above line 3 in FIG. 3, because acrylonitrile content in acrylonitrile polymers is small, a desirable result cannot be obtained. When the amount of acrylamide in A component increases within the area surrounded by lines 7 and 8 including line 7 and x and r are above line 3 in FIG. 3, not only are the difficulties in process controlling upon the preparation of polymers increased but it is also often observed that adhesion between monofilaments occurs in the drying step after the spinning step and thereby decisive obstruction is occasionally given to the crimping potential which is one of the important features of a composite fiber. In addition, a general degradation in thermostability, such as an increase in heat-coloring occurs. With any combination of two polymers, both of which are within the composition range for B component, crimp development is very slight, also, strain recovering property is inferior, substantiality is poor and no satisfactory product can be obtained. Also with any combination of two polymers, both of which are within the composition range for A component,

crimp development is again slight, also strain recovering property is generally not so good and is occasionally very inferior, depending on the conditions, and thus there are many difficulties in practical applications.

When composite filaments are produced using B component in which x and y are in the area surrounded by curves 1, 2 and 6 in FIG. 3 and A component in which x and t are within the area surrounded by curves 1, 2 and 3 in FIG. 3 and t and z are below curve 8 in FIG. 4, the strain recovering property at normal temperature, substantiality, thermal structure of fibrous articles prepared from said fiber, after being subjected to fixing treatment and so on are inferior to those obtained in the case of using polymers which are within the scope of our prior invention. In order to obtain some of said prop rties, it was required to employ a peculiar treating step carefully controlled in the process.

As mentioned above in detail, the effects of using combinations of two polymers of A component in which x and t are within the area surrounded by curves 1, 2 and 3 in FIG. 3 and t and z are within the area surrounded by lines 7 and 8 including line 7 in FIG. 4 and B component in which x and y are within the area surrounded by I, 2 and 6 in FIG. 3 are apparent. Further, one of the remarkable effects was that when using said combinations, it was possible to employ substantially the same process of preparing fiber as the process of preparing noncomposite fiber using concentrated nitric acid as solvent, that is, acrylonitrile common fiber, except for the point of using a special spinneret.

In particular, two kinds of polymers A and B described above are dissolved respectively in concentrated nitric acid aqueous solutions sufficiently refined to obtain two kinds of spinning solutions. The two kinds of spinning solutions are spun together through a special spinneret to obtain a gel yarnlike mass of a composite fiber, in which the two kinds of polymers are joined together eccentrically in the same single fiber section. The composite fiber is sufficiently washed with water, is stretched in hot water, is subjected to treatment with an oil agent and then is dried. The composite fiber after being once dried is supplied with an-oil agent again according to a spray method or a dip method and, after crimping or without crimping, is passed to a secondary drying step. The fiber which has completed the secondary drying is subjected to thermosetting in order to remove shrinkage and then, after crimping mechanically or without crimping, is cut down into staple fiber or consists of preliminary article as it is in tow form without cutting.

We have made further research and have found the surprising fact that if the once-dried fiber after spinning is passed through a high-temperature hot water bath without changing the tows linear speed and under a condition of substantially no relaxation nor tension before the secondary drying step, crimps develop in the final product, which is obtained after the secondary drying, a thermal setting to remove shrinkage and so on conducted in the same way as in the prior process, is greatly increased as compared to the prior process.

The extent of the increase in crimps is more or less variable, depending on the composition of the composite fiber, conditions of the process before introducing the fiber into the hot water bath, conditions of the process thereafter and so on. But depending on the use or nonuse of hot water bath treatment or extent of the treatment, the final product becomes a completely different material even when using composite fibers obtained by using the same composition of polymer and by making the remaining steps the same. Thus the effect of the hot water bath treatment is remarkable.

The higher the temperature through which the fiber is passed is, the greater the effect is. In cases of using water, a temperature from 65 to l C. is preferable. It is possible to raise the temperature by adding salts according to circumstances. Though, of course, the effect does not disappear below 65 C., the tendency to increase crimps decreases greatly compared to cases of higher temperature such as 90 C. or higher. Especially, at temperatures higher than 70 C.,

the efi'ect becomes remarkable. As to the time required for the hot water bath treatment, a short time such as ll0 seconds is sufficient to produce the effect. Also the speed at which the tow is passed through the hot water bath may be within the range usually employed industrially and in this case the fiber can be treated without any special devices.

The hot water bath treatment may be conducted in an apparatus such as shown in FIG. I. It is desirable to pass the tow at a speed as uniform as possible, that is, by avoiding stretching or relaxation shrinkage in the hot water bath. Desirably, the tension applied to tow is less than 5Xl0 gram/denier. As the tension increases, the effect of our invention decreases. We had previously found that if a composite fiber prepared according to wet spinning methods is once dried to a water content of lower than 15 percent, desirably to an absolutely dried state, and then is subjected to the hot water treatment under the condition of a tension lower than 5X10 g./denier to sufficiently effect relaxation shrinkage, the properties of the composite fiber can be greatly improved. But we did not anticipate that such advantages can be obtained only by passing the fiber through hot water at a substantially unchanged speed without allowing any relaxation.

It is not efi'ective to pass the fiber through steam at an unchanged speed instead of the hot water treatment. But, when after spinning and drying, a sufficiently relaxed fiber is used in steam at C., the effect of hot water treatment can be observed.

The increase in the crimp-producing ability according to the hot water treatment can be clearly observed in a composite fiber which has been provided with the secondary oil agent after the hot water treatment, subjected to the secondary drying, then subjected to thermosetting using steam or the like in order to remove shrinkage and then made into a tow or staple shape provided with or without mechanical crimp for ordering shape of product to be forwarded from the factory.

The thermosetting, using steam or the like, in order to remove shrinkage, may be conducted in the same was as is usually conducted for acrylonitrile fibers and special care is not required.

It is quite a surprising fact that the crimping degree may be varied by up to nearly 50 percent merely due to a difference in the temperature of the hot water treatment by about l040 C., even if the composite fiber is prepared by employing the same polymers, the same spinneret and the similar steps.

Thus, the increase in the crimping potential according to the hot water treatment makes it possible to very easily prepare composite fibers having various crimp characteristics using the same combination of polymers and it provides a means that is very important industrially.

The problems mentioned in the explanation of our prior invention, for example, the problem that it is difficult to obtain composite fiber having sufficiently satisfactory crimp properties by using two kinds of polymers in which it and y are within the area surrounded by curves 1, 2 and 6 in FIG. 3 are easily solved by adding the hot water treatment step to our invention.

In accordance with the present invention, polymers satisfying the following requirements must be used:

In A: x and t are within the area surrounded by 7 and 8 including 7.

In B: t and z are within the area surrounded by 7, 8 and the transverse axis. In addition, if the values of x, z and t for the A component are designated as xA, zA and IA and those for the B component are designated as X8, Z8 and IB, the above two polymers A and B must also satisfy the following simultaneous inequalities:

zA-1B l.0 preferably,

rArB l.2 The two polymers A and B are respectively dissolved in sufficiently refined 60 percent or higher concentrated nitric acid and are spun to be joined together eccentrically in fiber section by using a spinneret. The resultant composite fiber is sufficiently washed with water, then is stretched in hot water, is once dried to a water content of 15 percent or lower, desi ably 1 percent or lower, then is subjected to a hot water treatment, as mentioned before, and thereafter is treated in the same way as for usual noncomposite fibers. Thus, a composite fiber having various strong points of our prior invention can be obtained.

Further, in accordance with the present invention, by spinning the two kinds of polymers of our prior invention, that is, the polymers satisfying the following requirements:

In A: x and t are within the area surrounded by l, 2 and 3 in FIG. 3 and t and z are within the area surrounded by 7 and 8 including 7 in FIG. 4.

In B: x and y are within the area surrounded by I, 2 and 6 in FIG. 3.

And in addition t-z z and by subjecting the spun fiber to the hot water treatment, as mentioned before above, a composite fiber losing none of the advantages of our prior invention and having superior crimp properties can be obtained.

We have found that the closer the compositions of the two polymers to be bonded in the preparation of composite fiber are to each other, the better the balance of the properties of the fiber becomes and that one component in which it and y are within the area surrounded by 2, 3 and 4 in FIG. 3 and 1 and z are within the area surrounded by 7 and 8 including 7 in FIG. 4 and the other component in which x and l are within the area surrounded by l, 2 and 5 in 7 and 8 in FIG. 4, the two components satisfying formulas (I3), (14) and (15) can develop practical crimp properties for the first time by applying the hot water treatment of the present invention and give fibers having properties more excellent than the composite fiber which can be prepared according to our prior invention.

It is of course clear that the above-mentioned formulas are substantial to definitions of the polymer compositions and do not mean any strict range in a mathematical sense. The copolymer components to be used in the composite fiber include acrylamide, acrylates or methacrylates, methallyl sulfonic acid and acrylates or methacrylates of sulfoalcohols. The sulfonic acid may be in the form of free acid or its salts such as sodium salt, potassium salt or the like. Preferably, the sulfoalcohol is sulfoethanol, sulfopropanol, sulfobutanol or the like. When another ester such as vinyl acetate is used in place of acrylates or methacrylates such as methyl acrylate or methyl methacrylate, not only is splitting in the composite fiber likely to occur but also heat-coloring of fiber upon heat treatment conducted later becomes intensive. With styrene, the increase in substantiality is not enough and the fiber is brittle and it is difficult to obtain clear coloring after dyeing. Vinyl chloride, vinylidene chloride and the like are the same as styrene. With acids other than sulfonic acid such as itaconic acid, acrylic acid and other carboxylic acids, the whiteness of the fiber is bad, the fastness to sunlight of dyestuff after dyeing is not good and the quality of yarn is not preferable as a whole. As to sulfonic acid, when the composite filaments contain no acrylamide methallyl sulfonic acid and methacrylates or acrylates of sulfoalcohols are most preferable. The other sulfonic acids had apparent defects such as greatly lowering the stretching property upon spinning or extreme brittleness. But when x and t are between curves 4 and 5 and t and z are within the area surrounded by 7 and 8 including 7, except ones such as vinyl sulfonic acid greatly lower the stretching property in the spinning step, unless the hot water stretching property upon spinning is decisively bad for the combination of steps, there exists the characteristic that soft and stiff products having strain-recovering property can be obtained with any kind of sulfonic acid. At any rate, in respect to substantiality of the fiber, acrylates or methacrylates of sulfoalcohols give the best result and the next is methallyl sulfonic acid and there is observed some difference between said sulfonic acids and the other sulfonic acids.

In the present invention, it is of course clear that components other than the above-mentioned copolymer components may be introduced, for instance, during polymerization reaction or when dissolved in solvent to modify the polymer more or less and to add different kind of structure in the molecule or at the molecular ends and that very small amount of copolymerizable monomer as the fifth component may be introduced, without destroying the substance of the present invention. The polymers used as each component in the present invention are preferably copolymers. Blends of polymer are difficult to give satisfactory fibers in the points of substantiality and so on.

These polymers forming a composite fiber can be prepared by polymerization according to well-known methods. For instance, polymerization may be conducted by using as a polymerization initiator 2,2-azobisisobutyronitrile, benzoyl peroxide or hydroxynitrilo sulfonic acid-acid sodium sulfite and the like and by emulsion, suspension, solution polymerization or the like in medium or solvent such as water or organic compounds. The polymerization temperature is usually about 70 C. The operation system may be any of continuous system, semicontinuous system and noncontinuous system. Further, a polymerization regulator such as mercaptan may be added.

In the present invention, inorganic solvent" means concentrated solutions of inorganic acids such as nitric acid, sulfuric acid and the like or well-known inorganic substances such as potassium rhodanide, calcium rhodanide, zinc chloride, calcium chloride and the like. And tow concentrated nitric acid," which is especially prominent in the effect of the present invention, means nitric acid having a concentration of about 60-75 percent and refined to such an extent that the content of nitrogen oxides is less than about 0.0] percent. When dissolving acrylonitrile polymer in said concentrated nitric acid, it is preferable to maintain a temperature lower than 5 C. As a coagulating bath, usually nitric acid aqueous solution maintained lower than 5 C. and having 28-40 percent concentration is employed. FIG. 1 of the accompanying drawing shows hot-water treatment apparatus, but the apparatus may be modified variously within the scope of the present invention. In FIG. I, A are inlet rollers for the tow, B are outlet roller 5 for the tow, the arrow indicating the direction of movement, and C, C and C" are guide rollers disposed within a tank T. The four lines shown being passed from inlet rollers A through guide rollers C, C and C" to outlet rollers B are examples of possible engagement of the the with the guide rollers. It is possible to engage the tow with the guide rollers in other combinations of guide rollers. With in the scope of the present invention, many modifications of the tow engagement may be effected. FIG. 2 shows one example of a spinneret used upon working the present invention and shows only the principle simply for the purpose of clarification. In FIG. 2, spinneret surface plate (1) is attached to spinneret base (3) by means of bolt (2). Two kinds of spinning solutions A and B containing polymers different from each other are respectively introduced into space (4), (7) and (5), (6). The spinning solution in (4), (5) is transferred into space (8) and the spinning solution in (6), (7) is transferred into space (9) and the solutions are spun as yarnlike mass into outside coagulating bath respectively through spinnerets l0) and (11). In this case, outside the spaces (8) and (9) is filled the spinning solution introduced from the spaces (4) and (7) and inside the spaces (8) and (9) is filled the spinning solution introduced from the spaces (5) and (6). When spun from spinneret (10) or (11), the bath spinning solutions A and B are bonded together bimetallically to form a composite fiber. Of course, by changing the spinneret, it is possible to obtain composite yarn having sheath core structure or having desired shape of fiber section such as round, flat so on. W hin bimetallic type, it is possible to take sandwich type more or less depending on the conditions of spinneret.

The ratio between the both components in the present invention is possible to be about 20/80 to 80/20 and usually substantially equal amounts are employed. if required. this ratio may be varied along the direction offiber axis The spun composite fiber is coagulated into the form of yarn, is subjected to steps such as water washing and thermal stretching, and then is subjected to drying and heat treating, and further, if required, it is subjected to oil agent treatment, sizing and the like to be made into form of tow, cut fiber or continuous filament (long fiber). The following examples nearly illustrate the present invention without restricting same.

EXAMPLE 1 Four kinds of polymers were prepared using hydroxynitrilo monosulfonic acid and acid sodium sulfite as polymerization initiator.

The combinations of polymers for the preparation of composite fiber are as follows:

In the cases of applying no hot water bath treatment of the present invention, (lV) produced much fly in the spinning step and carding step and good spun yarn was not obtained. The composite fiber number (IV) gave a large proportion of broken fiber in the result of ball mill test conducted for this staple, and gave no clear coloring in the result of dyeing test conducted using Sevron Green B.

TABLE 1 Sulfoethy Acrylo- Acrylic Methyl methl Polymer nitrlle amide acrylate acrylate sign a: and! t and 2 (percent) (percent) (percent) (percent) a Area surromded by Below 7 and 8 91. 5 0 8. 0 0. 5

an b Area surrounded by Area surrounded by 7 89. 95 6. 9 2. 7 0. 45

2, 3 and 4. and 8 including 7. c ..do Below 7 and 8 89. 95 2. 7 6. 9 0.45 d Area surrounded by 95.1 0 4. 1 0.8

1, 2 and 6.

These polymers were dissolved in refined 72 percent nitric acid at l0 C. to 18 percent polymer concentration and spun through L200 hole spinnerets for composite fiber into 28 percent nitric acid at l0 C. to make composite yarnlike mass in such a way that the two components combined are in equal amount to each other. The composite fiber was washed with water sufficiently and then was stretched to eight times the original length in hot water at 98 C. to be 3 denier. After a conventional oil agent treatment, the fiber was dried and thereafter was treated in the similar way as treatments for a usual acrylonitrile fiber which is not a composite fiber, that is, it was subjected to heat treatment to remove shrinkage or was not, then was provided with mechanical crimp and was cut down to give average fiber length 102 mm.

One part of the tow after being spun was, after a conventional oil agent treatment and drying, passed into a hot water bath under a tension less than 0.005 grams/denier for about 2 seconds without giving any special relaxation to the tow according to the present invention, and was, after oil agent treatment and the secondary drying, made into composite fiber having average fiber length 102 mm. in the same way as above.

One part of this staple was subjected to various tests including determination of mechanical properties such as strength and elongation; test on brittleness by means of ball mill, dyeing test; test on production of natural crimp when subjected to heat treatment; test on yarn split at banded part when applying repeating stress to sample in which crimps are produced; test on crimp development when boiled under severe load permitting no crimp development for an hour and then, after removal of load, treated in hot water at 90 C. or steam at 100 C.; and major part of this staple was transferred through card to spinning step. In the spinning step, two folded yarns of metric yarn count 22 were respectively spun. In that time, there were made broad examinations on production of fly, spun state of spun yarn snapping, yam face and further behavior of the spun yarn when dyed, problems upon knitting and weaving, determination of physical properties of product such as hand-knit yarns, knittings and fabrics and so on. Hereinafter the results will be described.

The above four kinds of composite fibers were placed in hot water at C. and the extent of crimps developed in free condition was examined. As a result, the fibers (l) and (ll) gave very few crimp development. Then, crimp development fibers were made into bundles each of which consists of about l00 fibers, and the bundles were subjected to 15 cycles of repeated strain [(length at which crimp exists stably (length of crimp when disappearing +O,5 percent length)] using tensile testing machine designed as one of fix points takes sine reciprocating motion at desired amplitude, and then subjected to steam treatment at C. Further said operation was repeated 15 times. After said test the proportions of fiber damage and yarn split were counted in photograph of fiber and brittleness was examined. The results are summarized together with the results of ball mill test and amount of fly upon spinning in the following table.

The fiber (Ill), which gave good results in the above tests, belongs to the scope of our prior invention. The fibers (l) and (ll) could not be compared in the point that crimp development was few. The fiber (lV), which is apparently outside the scope of our prior invention, was slightly bad.

Further, in the results of examining change in crimping potential when raw cotton was boiled under severe load at 100 C. for 1 hour and then removed from the boiling bath and dipped in hot water at 90 C. for 5 minutes, the fibers (I) and (III) were superior and the fibers (II) and (IV) gave no good results.

In the results of examining stress-strain behavior, feeling and touch, etc. of hand-knit yarn articles, fabrics and knittings obtained using said fibers, only the fiber (lll) gave excellent results.

Further, according to the present invention, the tow, which had been spun from a special spinneret, washed with water and then subjected thermal stretching, oil agent treatmen' \nd the primary drying, was passed through hot water bath at constant speed under a tension less than X10 gram/denier, continuously dipped in the secondary oil agent bath at 65 C. under tension of 2X10 gram/denier, provided with crimp by means of crimper, dried at 110 C., and then subjected to batch-wise treatment with steam at 120 C. to remove shrinkage. This sample was stretched in yarn way and provided with mechanical crimp while ordering shape of tow. Shrinkage ration of said sampler when boiled freely in hot water and then dried at 70 C. were determined. As a result, it was found that crimping potential is greatly increased due to the hot water bath treatment and shrinkage ratio becomes large. The data on composite fiber sample (1) are shown in the following table.

TABLE 4 10 to 7.5 times in hot water, provided with oil agent and then dried. The tow dried was passed continuously through hot water bath at 60100 C. under tension of 1.2X10 gram/denier at substantially constant speed over about 3 seconds, treated with oil agent again and then dried. The dried tow was subjected to heat treatment for removing shrinkage and provided with mechanical crimp, according to conventional procedures. When making spun yarn or other fibrous articles, said tow was cut as required and then used.

When the tow before cutting was heated in free state with steam, hot water or the like, shrinkage due to crimp develop- Shrinkage ratio my 103d ment occurred. The extent of said shrinkage was varied widely Temperature of whenrgrtaitgz-(nlggilr g s ggnkage depending on temperatures of hot water treatment in the n water bath present invention. The results are shown in the following tatreatment C.) 10 50 200 TABLE 6.SHRINKAGE RATIO (PERCENT) r Load when determining shrinkage ratio (mg/denier) From the results in the above table, the effect of hot water & bath treatment is apparent and it is understood that the fiber (l), which was before considered to be insutficient in crimping $8 g g-g potential, can be developed to have sufficiently practical Hot Water i g 1 7 111'5 4: 7 crim in r0 ert temperature 90 24.2 14.6 5.2 p gp p 100 303 18.9 6.0 Spun yarns obtained using only the fiber (l) which had been subjected to hot water bath treatment at 80 C. were made into various articles. Separately spun yarns obtained using mixture of 50 percent of the fiber (l) which had been subjected to hot water bath treatment at 100 C. and 50 percent 40 From the above tows treated with hot water at different of a usual acrylic fiber which was not a composite fiber were 0 e temperatures, samples treated at 80 C. and 100 C. were made into various articles. On the other hand, composite taken up and cut down to average length 102 mm. These fibers (l)-(IV) prepared not according to the present invenfibers were mlxed with 0 percent, 10 percent, 20 percent, 30 tion were made into fibrous articles. These articles were com- 40 50 d 60 percent, percent, percent an percent noncomposite l The p prepared accprdmg. to the present mven' usual acrylic fiber respectively and were spun together. Bulk tion were superior in bulk producing ratio by about 20-10 perh th d d d b k d tin average when the articles were boiled for about 1 hour i w en e spun yar-ns were an y we [h f h k d th t d were 1nd1cated by values of shrinkage ratio for convenience, a un er 6 con 1 O i mg 5 rm en Jec e part of which are shown in the following table. The determina- Stem. under fieejmndmon X those prepared tion of shrinkage ratio was made by measuring length (L 200) otherwise Herefn bulk pfoducmg rat) means of spun yarn before bulkylized under load of 200 mg./denier of shrinkage ratio when boiled for 1 hour under the condltion and length (L 37 5) of spun yam after bulkylized under load of shnnkage dned wnh at 70 and of 37.5 mgJdenier and by calculating according to the followtreated with steam at 100 C. for 10 minutes under free condling formula. tion, based on shrinkage ratio (100) when boiled for one hour under the condition of not limiting shrinkage and then dried L 200 37 5 with hot air at C. Further, in any aspect such as strain- Shrinkage X 100 recovering property, substantiality, dyeability, the articles according to the present invention gave the same or better TABLE 7 SHRINKAGE RATIO (PERCENT) results compared with the best article (Ill) prepared not ac- 60 fl d cording to the P invention 10 20 30 40 50 60 Samples treated with hot water at C. 19 17. 5 15 Samples treated with hot water at 100 c 19.5 18 15 EXAMPLEZ W H The following polymers were prepared using, 2,2'-azobi- 65 As is apparent from the above table, it is possible to prepare sisobutyronitrile as polymerization initiator. raw cotton suitable for manufacture comprising mix spinning TABLE 5 Sodium Acrylo- Acrylic Methyl methallyl Polymer nitrile amide acrylate sulfonate sign I and! t and 2 (percent) (percent) (percent) (percent) 9 Area surgognded by Below 7 and 8 91.00 0 8. 50 0.60

1, an 1 Area surrounded by Area surrounded by 7 89. 9. 72 0 0. 38

2, 3 and 4. and 8 including 7.

at high proportion composite fiber and raw cotton suitable for manufacture comprising mix spinning st low proportion of composite fiber from the same combination of polymers by utilizing difference of hot water treatment.

the spun, once-dried fiber through a hot water bath substanto the spinning speed.

2. An improvement as claimed in claim 1 in which the inor- EXAMPLE 3 ganic solvent is a concentrated nitric acid solution.

The following polymer was prepared by using hydrox- 3. An improvementasclaimed in claim 1 in which the spun, ynitrilo monosulfonic acid and acid sodium sulfite as once-dried fiber is passed through the hot water bath for a polymerization intiator. period from 1 to seconds.

TABLE 8 Sodium Acry1o- Acrylic Methyl methallyl Polymer nitrile amide acrylate sulfonate Sign .Z and t t and 2 (percent) (percent) (percent) (percent) g Area surrounded by Area surrounded by 7 89. 95 6. 90 2. 70 0. 45

2, 3 and 4. and 8 including 7.

Using said polymer 3. and the polymer a in example 1 and in 4. An improvement as claimed in claim 1 in which the spun, the similar way as in example 2, were prepared composite 20 once-dried fiber hasawater content lower than percent. fibers. The composite fiber were different from each other in 5. An improvement as claimed in claim 1 in which the ratio shrinkage ratio depending on the temperature of hot water of the two polymers is from /80 to 80/20. treatment, were enhanced in substantiality and were good in 6. In the process for preparing a composite acrylonitrile strain recovering property. fiber in which two kinds of acrylonitrile polymers are bonded We claim: together eccentrically in fiber section by a wet spinning 1. In a process for preparing a composite acrylonitrile fiber method using an inorganic solvent, an improvement which in which two kinds of acrylonitrile polymers are bonded comprises employing two kinds of polymers A and B which together eccentrically in fiber section by a wet spinning simultaneously satisfy the following inequalities: method using an inorganic solvent, and improvement which for component A; comprises employing two kinds of polymers A and B which 0.55 cot l.57 )!+5.6 0 (l) simultaneously satisfy the following inequalities: 700x +t-423 O (2) Component A; 0.83x+l1 l.5 0 (3) for component B; 0.55 cot (1.57x)t+6.6 0 (9) (4) 700x+y423 0 (5 700x+t 423 0 (2) 1.57 exp.y0.35 0 (6) 0.83x+t l1.5 0 (3) and in addition;

f 2 t z -l 4 8, W5... .113 (8) for Component B;

wherein X is the weight percentage of at least one member 0'55 cot (157x) t+5'6 0 (1) selected from the group consisting of methallyl sulfonic acid 700x+t423 0 and acrylates and methacrylates of sulfoalcohols contained in O.83a:+t 10.5 0 (10) the polymers, Y is the weight percentage of at least one t z 0 (11) member selected from the group consisting of acrylates and methacrylates contained in the polymers, 1 is the combined i z 5 exp. (4 )2} 0 5 weight percentage of acrylamide and at least one member 4 (12) selected from the group consisting of acrylates and methacryd i dditi lates contained in the polymers, Z is the weight percentage of acrylamide contained in component A, the remainin arts of XA XB S 0 (13) component A and component B being acrylonitiife, and Z Z 6 (14) passing the spun, once-dried fiber through a hot water bath 1 (15) substantially without relaxation and tension of less than 5Xl0 gram/denier and at a substantially unchanged speed relative to the spinning speed. wherein X is the weight percentage of at least one member 7. An improvement as claimed in claim 6 in which the inorselected from the group consisting of methallyl sulfonic acid ganic solvent is aconcentrated nitric acid solution. and acrylates and methacrylates of solfoalcohols contained in 8. An improvement as claimed in claim 6 in which the spun, the polymers, r is the combined percentage by weight of once-dried fiber is passed through the hot water bath for a acrylamide and at least one member selected from the group P d fr m 1 l0 l0 e dconsisting of acrylates and methacrylates contained in the An mpr m nt as c m d in Claim 6 in which the spun, polymers, Z is the percentage by weight of acrylamide con- Once-dried fiber hasawater content lower than 15 percent. tained by the polymers, subscript A in X and 2,, represents 10. An improvement as claimed in claim 6 in which the ratio the values for component A, the remaining parts of comofthe two p y is from 20/80 to ponents A and component B being acrylonitrile, and passing t 

2. An improvement as claimed in claim 1 in which the inorganic solvent is a concentrated nitric acid solution.
 3. An improvement as claimed in claim 1 in which the spun, once-dried fiber is passed through the hot water bath for a period from 1 to 10 seconds.
 4. An improvement as claimed in claim 1 in which the spun, once-dried fiber has a water content lower than 15 percent.
 5. An improvement as claimed in claim 1 in which the ratio of the two polymers is from 20/80 to 80/20.
 6. In a process for preparing a composite acrylonitrile fiber in which two kinds of acrylonitrile polymers are bonded together eccentrically in fiber section by a wet spinning method using an inorganic solvent, an improvement which comprises employing two kinds of polymers A and B which simultaneously satisfy the following inequalities: for component A; 0.55 cot (1.57x)-t+5.6<< 0 (1) 700x +t-423<0 (2) 0.83x+t-11.5<0 (3) for component B; 0.55 cot (1.57x)-y+5.6>0 (4) 700x+y-423>0 (5) 1.57 exp. -y-0.35<0 (6) and in addition;
 7. An improvement as claimed in claim 6 in which the inorganic solvent is a concentrated nitric acid solution.
 8. An improvement as claimed in claim 6 in which the spun, once-dried fiber is passed through the hot water bath for a period from 1 to 10 seconds.
 9. An improvement as claimed in claim 6 in which the spun, once-dried fiber has a water content lower than 15 percent.
 10. An improvement as claimed in claim 6 in which the ratio of the two polymers is from 20/80 to 80/20. 